The architecture and the design of modern radio access networks, such as UTRAN (UMTS terrestrial radio access networks; UMTS: Universal Mobile Telecommunications System) become more and more complex. The overall mobile radio systems have a lot of different entities, devices and components, namely user terminals, radio base stations, at least one radio network controller for controlling a cluster of radio base stations, and switching devices, such as a mobile switching center for establishing circuit-switched connections to public switched telephone networks (PSTN) or the like. Also routers for establishing packet-switched connections to IP based networks, esp. to the world wide web, may be installed as well.
Basically the base stations and the radio network controller are constituting the radio access network which is also referred to as RAN. The switching devices are constituting the so-called core network. The interface between the RAN and the core network is quite complex, in the case of UTRAN an so-called Iu interface is used as being defined by the ETSI document 3GPP TS 25.410 having the title “UTRAN Iu Interface: general aspects and principles”.
The RAN is providing mobile radio services to a wide geographical area which is divided into a multiplicity of radio cells. Every cell is controlled by a base station, and each base station controls at least one radio cell. In the UTRAN which is operating in accordance with the UMTS standard the base stations are referred to as node B. The base stations support the connection establishment to the terminals and establish the connections to a plurality of terminals in a radio cell. The connection has the form either of a permanent connection for the transmission of circuit switched data or a non-permanent connection for the transmission of packet switched data. The data signals transmitted via the connection are representing all kind of communication data, such as voice, audio, text, video data or other kinds of user data.
The network elements for controlling the radio cell clusters are the radio network controllers, also referred to as RNC. Each RNC is assigned to a plurality of base stations, typically up to few hundred base stations. The RNC performs for example the radio resource management and the terrestrial resource management of a radio cell cluster. In particular, the RNC controls transmission power on radio bearers, handovers (transfer of a terminal from one radio cell into another) as well as the macro diversity mode.
The RNC is connected via interfaces to the other network elements. In UMTS this means that a RNC comprises at least one Iu-interface to a core network, possibly one or several Iur-interface to another RNC, at least one Iub interface to a base station (e.g. to a Node B), and at least one logical interface to a terminal UE which leads physically across the Iub-interface or the Iub and Iur interfaces .
In the existing radio access networks, such as the conventional UTRAN, all control and user plane information relative to a particular user terminal or to a certain area are exchanged via the Iu interface between the core network and the radio network controller which is the serving controller for this user terminal. In an evolved UTRAN, it is foreseen that the radio network controller is split in its control and user planes, which are located in different network elements, herein also called radio network controlling elements.
The principle of this clear separation between the control and user planes is shown in the FIGS. 1a/b. As can be seen from FIG. 1a the user plane contains all the channel processing, e.g. header compression, radio link control, channel multiplexing and macro-diversity combining. The control plane encompasses all signaling related processing for application protocols, such as NBAP (Node B Application Part), RNSAP (Radio Network System Application Part) and RANAP (Radio Access Network Application Part) on the RAN-CN interface, and also signaling for radio resource control of the air interface (RAN-UE interface, i.e. Uu).
This separation allows to separately scale both planes, what results in turn in a better scalability for the whole system. With the split of the RNC, the RAN will be based on a higher number of smaller and simpler network elements as shown in FIG. 1b. 
However, this separation also implies a higher number of hardware elements resulting in a higher number of external interfaces; some of them are new and must be defined. The split of control and user planes has also a certain impact on QoS (Quality of Service) provisioning, a problem which must be analyzed and solved in detail.
The RNC as shown in FIG. 1b is complex assembly of a control plane server CPS and a plurality of user plane servers UPS for carrying out control or user plane functions respectively. These different types of servers perform many different and sometimes unrelated functions. This introduces extra complexity in the design of the RAN and even more of the whole mobile radio system.
If both planes are split, the Iu, Iur and Iub interfaces are also split in their control and user plane components as can be seen from FIG. 1a. However, this does not require changes in the RNC architecture, since different protocols for the control and the user plane are already used for these interfaces. The control parts of the interfaces would include the different application parts (so-called RANAP, RNSAP and NBAP), whereas the bearer parts would contain the different frame protocols.
Signaling between the RAN and the UE is also considered as belonging to the control plane. Therefore, the RRC (Radio Resource Control) protocol is terminated in the control plane, whereas layer 2 protocols (RLC, MAC) and macrodiversity combining and splitting are located in the user plane.
The split RNC is connected via a modified Iu* interface which has to manage the exchange of information and control signals between the core network CN and a lot of different RNC elements, namely the CPS and UPS servers. The more servers are needed to realize the whole RNC the more complex is the design of the Iu* interface.
In an evolved RAN architecture as shown in FIGS. 1a/b, the user and the control planes are separated into different network elements. This implies that the core network CN must exchange control and user information related to a particular user terminal UE with two different network elements. Moreover, information not linked to a particular user but to a certain cell or area (e.g. paging or cell broadcast service) must also be directed to the appropriate control or user plane server(s).
With the suggested split of the RNC functions, there appears the need for a solution to minimize the impact on the RAN-CN interface., i.e. the Iu interface. In this respect it would be desirable to make use of a standard interface, such as that Iu interface which is known from UMTS. Further there seems to be a need for a new RNC internal interface to manage better the exchange of data between the UPS and CPS elements. This interface should be able to transport at least control information for the configuration of user plane elements and feedback information such as status, error or event reporting, etc.
Therefore the object of the invention is to overcome the drawbacks as mentioned above and to present an advantageous design for a new radio access network which can easily be connected to the core network.